A Machine Gun Company was attached to each Infantry Brigade and their subsequent Division.
| Brigade attached to: | 12th Brigade |
| Division attached to: | 4th Division |
| Formed from the: | Machine Gun Section of 1st Bn. The King's Own (Royal Lancaster Regiment) |
| Machine Gun Section of 2nd Bn. The Lancashire Fusiliers | |
| Machine Gun Section of 2nd Bn. The Essex Regiment | |
| Machine Gun Section of 2nd Bn. The Monmouthshire Regiment |
The 12th Bde. M.G. Coy. was formed on the 24 January 1916 from the Machine Gun Sections of the listed infantry battalions.
On 26 February 1918, it was amalgamated with the 10th, 11th and 234th Machine Gun Companies to form No. 4 Battalion, Machine Gun Corps.
As a unit of the 4th Infantry Division, it will have taken part in the following battles and engagements.
| 1916 | |
| BATTLES OF THE SOMME | |
| From 01 to 21 July | [VIII. Corps, Fourth Army; then from 03 July VIII. Corps, Reserve Army] |
| FRom 10 to 25 October | [XIV. Corps, Fourth Army] |
| 01 and 02 July | Battle of Albert [VIII. Corps, Fourth Army]. |
| 10 to 18 October | Battle of the Transloy Ridges [XIV. Corps, Fourth Army]. |
| 1917 | |
| BATTLES OF ARRAS | |
| 09 to 14 April | First Battle of the Scarpe [XVII. Corps, Third Army]. |
| 03 and 04 May | Third Battle of the Scarpe [XVII. Corps, Third Army]. |
| BATTLES OF YPRES | |
| 28 September to 03 October | Battle of Polygon Wood [XIV. Corps, Fifth Army]. |
| 04 October | Battle of Broodseinde [XIV. Corps, Fifth Army]. |
| 09 October | Battle of Poelcappelle [XIV. Corps, Fifth Army]. |
| 12 October | First Battle of Passchendaele [XIV. Corps, Fifth Army]. |